1. Field of the Invention
In one aspect this invention relates to supplemental heaters for use in vehicles. In a further aspect, this invention relates to multifuel heaters using an external combustion air supply and external exhaust for use in heating vehicles.
2. Prior Art
The use of a supplementary, forced air heater in vehicles is well known. In military vehicles such heaters are subjected to unusual extremes of environmental conditions including excessive dust. The conditions are much more extreme than those encountered by normal vehicles which makes normal commercial heaters inefficient and short lived.
One example of a commercial air heater is disclosed in U.S. Pat. No. 3,523,004. This Patent discloses a heater configuration with a casing forming a combustion chamber and having an associated blower for forcing combustion air longitudinally through the combustion chamber. The burner has an internal apertured plate located transversely across the casing to direct the combustion air along predefined longitudinal paths. A cupped shaped number is positioned down stream from the plate with its open end facing toward the apertured plate to receive the combustion air. A wick is coaxially mounted in the combustion chamber and is connected to a fuel source which feeds liquid fuel to the wick for vaporization and combustion.
Burners of this general configuration have provided good performance characteristics under various conditions; however, they have problems with the dust and debris commonly encountered under battlefield conditions. The debris and dust particles entering the heater tend to accumulate in the bottom of the vaporizing cup. This results in constricted air flow and impedes the heater's flame path as the flame exits the vaporizing shield. The dirt and any unburned combustion product also eventually coat the porous fuel vaporizer. In extreme cases, the dirt will block the fuel vaporizer to the extent the heater can not function adequately. The heater must then be rebuilt before the end of its normal life cycle.
This problem is particularly acute since the combustion air must be drawn from the ambient surroundings and can not be filtered. Filtration of the combustion air is not practicable on military vehicles since filtration would cause a pressure drop in the air intake and require frequent filter changes.